/usr/include/firefox/vpx/ is in firefox-dev 11.0+build1-0ubuntu4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/firefox/vpx/arm.h
/usr/include/firefox/vpx/config.h
/usr/include/firefox/vpx/mem.h
/usr/include/firefox/vpx/scale_mode.h
/usr/include/firefox/vpx/vp8.h
/usr/include/firefox/vpx/vp8cx.h
/usr/include/firefox/vpx/vp8dx.h
/usr/include/firefox/vpx/vp8e.h
/usr/include/firefox/vpx/vpx_codec.h
/usr/include/firefox/vpx/vpx_codec_impl_bottom.h
/usr/include/firefox/vpx/vpx_codec_impl_top.h
/usr/include/firefox/vpx/vpx_decoder.h
/usr/include/firefox/vpx/vpx_decoder_compat.h
/usr/include/firefox/vpx/vpx_encoder.h
/usr/include/firefox/vpx/vpx_image.h
/usr/include/firefox/vpx/vpx_integer.h
/usr/include/firefox/vpx/vpx_mem.h
/usr/include/firefox/vpx/vpx_mem_intrnl.h
/usr/include/firefox/vpx/vpx_timer.h
/usr/include/firefox/vpx/vpxscale.h
/usr/include/firefox/vpx/x86.h
/usr/include/firefox/vpx/yv12config.h
/usr/include/firefox/vpx/yv12extend.h